The present invention relates to a damping force control type shock absorber capable of controlling damping force.
Shock absorbers attached to suspension systems of automobiles or other vehicles include a damping force control type shock absorber designed to be capable of appropriately controlling damping force in accordance with road surface conditions, vehicle running conditions, etc. to improve ride quality and steering stability.
In general, the damping force control type shock absorber includes a cylinder having a fluid sealed therein. A piston connected with a piston rod is slidably fitted in the cylinder. A damping force control mechanism is provided in a passage through which the fluid flows in response to sliding movement of the piston in the cylinder. Japanese Patent Application Publication No. 2001-12534 discloses a damping force control mechanism that generates damping force by controlling the flow of fluid through a pilot-type damping valve and that further controls the damping force by controlling an actuator-driven control valve provided in a passage through which the pilot pressure is discharged.
The damping force control mechanism disclosed in Japanese Patent Application Publication No. 2001-12534 suffers, however, from the problem that the control valve is undesirably closed when the actuator is unenergized owing to a failure or the like, resulting in the damping force becoming excessively high.